For most people, routine STI screening is just one more part of staying on top of your health. And depending on your lifestyle and risk factors, what you get tested for and when may vary. You might just be tested for chlamydia, gonorrhea, and HIV. Or you might also be tested for things like syphilis and hepatitis B. But what about hepatitis C?

Hepatitis C is a liver infection that you can have for years and never realize it.

But, left undetected, hepatitis C can cause serious health complications like scarring of the liver, liver cancer, and liver failure, which can be deadly. So, of course, it's important to know if you have it sooner rather than later.

You probably never considered hepatitis C as an STI because it’s not commonly passed on via sex. According to the Mayo Clinic, the people who are at most risk of contracting hepatitis C are those who have injected drugs, received a piercing or tattoo using unsterile equipment, received a blood transfusion or organ transplant before 1992 (when widespread screening began for hepatitis C), were born to a woman with a hepatitis C infection, or were born between 1945 and 1965 (as this age group has the highest incidence of hepatitis C infection).

Hepatitis C is a bloodborne virus, meaning it’s contracted through exposure to small quantities of blood. That can make the sexual transmission part confusing, but Amesh A. Adalja, M.D., senior associate at the John’s Hopkins Center for Health Security, tells SELF that hepatitis C transmission during sex generally occurs through some sort of trauma during intercourse (like tearing) and it’s usually due to anal sex, he says. There are a lot of blood vessels in a person’s anus, and tearing during anal sex can lead to bleeding, which could then transmit the virus if one person is infected, Dr. Adalja explains.

The risk of hepatitis C transmission during sex between heterosexual partners is rare, particularly if you're in a long-term relationship with one partner and neither partner has HIV. However, the risk increases if one or both partners has HIV or multiple sexual partners, according to the CDC.

There were an estimated 30,500 new cases of hepatitis C reported in 2014, and up to 3.9 million people in the U.S. have chronic hepatitis C. But currently the biggest risk factor of hepatitis C is injection drug use. It's worth pointing out that the CDC has noted a small but significant uptick in cases of pregnant women with hepatitis C, especially among white women who live in rural areas. However, this may not be linked to sex. Researchers note that this coincides with the rising heroin and prescription opioid epidemic, which also disproportionately affects white and rural populations.

According to the Mayo Clinic, a person can have hepatitis C for years and not have any symptoms. But, once they do develop symptoms, they typically include bleeding easily, bruising easily, fatigue, a poor appetite, jaundice (i.e. yellow discoloration of the skin and eyes), dark-colored urine, itchy skin, weight loss, and swelling in the legs.

If you suspect that you may have hepatitis C, have had unprotected sex recently, used injection drugs, or have a partner with hepatitis C, ask your doctor about getting tested. The infection is curable thanks to antiviral therapy, says Dr. Adalja, but it can cause damage the longer it goes undetected.